Navy Yard shooting in Washington DC

A U.S. Park Police helicopter flies over a building at the Washington Navy Yard in Washington, Monday, Sept. 16, 2013. President Barack Obama is mourning what he called "yet another mass shooting" in the United States that he says took the life of American patriots. (AP Photo/Susan Walsh)

AP

U.S. Capitol Police personnel keep watch on the East Plaza of the Capitol as the investigation continues to the shooting at the nearby Washington Navy Yard Monday, Sept. 16, 2013, in Washington. At least one gunman opened fire inside a building at the Washington Navy Yard on Monday morning, and officials said six people were killed and as many as 10 were wounded, including a law enforcement officer. (AP Photo/J. Scott Applewhite)

AP

Armed police prepare to enter the Washington Navy Yard as they respond to a shooting in Washington, Monday, Sept. 16, 2013. At least one gunman opened fire inside a building at the Navy yard. (AP Photo/Manuel Balce Ceneta)

AP

Law enforcement personnel gather outside the gate of the Washington Navy Yard in Washington, Monday, Sept. 16, 2013. At least one gunman opened fire inside a building at the Washington Navy Yard on Monday morning. (AP Photo/Susan Walsh)

AP

A police boat and helicopter patrol near the scene of a shooting at the Washington Navy Yard on Monday, Sept. 16, 2013, in Washington. At least one gunman opened fire inside a building at the Washington Navy Yard, and officials said six people were killed and as many as 10 were wounded, including a law enforcement officer. (AP Photo/ Evan Vucci)

AP

President Barack Obama speaks in the South Court Auditorium on the White House complex, Monday, Sept. 16, 2013, in Washington. Before speaking about the economy Obama commented on the Washington Navy Yard shooting. (AP Photo/Carolyn Kaster)

AP

This photo, which AP obtained from Don Andres and has been authenticated based on details in it, shows emergency personnel attending to a scene where a gunman was reported at the Washington Navy Yard in Washington, on Monday, Sept. 16, 2013. At least one gunman opened fire inside a building at the Washington Navy Yard on Monday morning, and a Defense Department official said several people were killed and as many as 10 were wounded, including a law enforcement officer. (AP Photo/Don Andres)

AP

A U.S. Park Police helicopter flies over a building at the Washington Navy Yard in Washington, Monday, Sept. 16, 2013. At least one gunman opened fire inside a building at the Washington Navy Yard on Monday morning, (AP Photo/Susan Walsh)

AP

Airplanes wait near the runway at Washington Reagan National Airport after the airport was shutdown for over an hour on Monday, Sept. 16, 2013 in Washington. (Kevin Wolf/AP Images for HHMI)

FR33460 AP

District of Columbia Police Chief Cathy Lanier briefs reporters on the shooting at the Washington Navy Yard in Washington, Monday, Sept. 16, 2013, where at least one gunman opened fire inside a building at the Washington Navy Yard. (AP Photo/Susan Walsh)

AP

District of Columbia Police Chief Cathy Lanier briefs reporters on the shooting at the Washington Navy Yard in Washington, Monday, Sept. 16, 2013. Standing to the right of Lanier is District of Columbia Mayor Vincent Gray. At least one gunman opened fire inside a building at the Washington Navy Yard on Monday morning (AP Photo/Susan Walsh)

AP

U.S. Capitol Police personnel keep watch on the East Plaza of the Capitol as the investigation continues at the nearby high-security Washington Navy Yard where gunmen went on a shooting rampage, Monday, Sept. 16, 2013, in Washington. (AP Photo/J. Scott Applewhite)

AP

An officer stands near the gate of the Washington Navy Yard in Washington, Monday, Sept. 16, 2013, after a gunman opened fire. (AP Photo/Susan Walsh)

AP

A police boat patrols near the scene of a shooting at the Washington Navy Yard on Monday, Sept. 16, 2013, in Washington. At least one gunman opened fire inside a building at the Washington Navy Yard, and officials said six people were killed and as many as 10 were wounded, including a law enforcement officer. (AP Photo/ Evan Vucci)

AP

A U.S. Park Police helicopter circles the Washington Navy Yard Monday, Sept. 16, 2013, after a gunman was reported at the Navy Yard. Earlier in the day, the U.S. Navy said it was searching for an active shooter at the Naval Sea Systems Command headquarters, where about 3,000 people work. The exact number of people killed and the conditions of those wounded was not immediately known. (AP Photo/Jacquelyn Martin)

AP

A U.S. Capitol Police armored vehicle patrols the East Plaza of the Capitol in front of the Senate as the investigation continues at the nearby high-security Washington Navy Yard where gunmen went on a shooting rampage, Monday, Sept. 16, 2013, in Washington. (AP Photo/J. Scott Applewhite)

AP

U.S. Park Police helicopters circle the Washington Navy Yard Monday, Sept. 16, 2013, after a gunman was reported at the Navy Yard. Earlier in the day, the U.S. Navy said it was searching for an active shooter at the Naval Sea Systems Command headquarters, where about 3,000 people work. The exact number of people killed and the conditions of those wounded was not immediately known. (AP Photo/Jacquelyn Martin

AP

U.S. Capitol Police personnel keep watch at the Constitution Avenue entrance to the East Plaza of the Capitol as the investigation continues at the nearby high-security Washington Navy Yard where a gunman went on a shooting rampage, Monday, Sept. 16, 2013, in Washington. (AP Photo/J. Scott Applewhite)

AP

District of Columbia Mayor Vincent Gray briefs reporters on the shooting at the Washington Navy Yard in Washington, Monday, Sept. 16, 2013. At least one gunman opened fire inside a building at the Washington Navy Yard on Monday morning. (AP Photo/Susan Walsh)

AP

Dr. Janis M. Orlowski, chief operating officer at Washington Hospital Center speaks at a news conference in Washington, Monday, Sept. 16, 2013, about the conditions of the people who were brought to the hospital from the shooting at the Washington Navy Yard building. Orlowski said the hospital was treating three gunshot victims in critical condition. One was Washington, D.C., metropolitan police officer and two were civilian women. (AP Photo/Jose Luis Magana)

FR159526 AP

Security personnel respond near the Washington Navy Yard where a gunman was reported in Washington, on Monday, Sept. 16, 2013. At least one gunman opened fire inside a building at the Washington Navy Yard on Monday morning, and officials said six people were killed and as many as 10 were wounded, including a law enforcement officer. (AP Photo/Manuel Balce Ceneta)

AP

U.S. Capitol Police personnel keep watch on the East Plaza of the Capitol as the investigation continues to the shooting at the nearby Washington Navy Yard Monday, Sept. 16, 2013, in Washington. At least one gunman opened fire inside a building at the Washington Navy Yard on Monday morning. (AP Photo/J. Scott Applewhite)

AP

Members of the military guard a military garage near the Washington Navy Yard where a gunman was reported in Washington, on Monday, Sept. 16, 2013. The exact number of people killed and the conditions of those wounded was not immediately known. (AP Photo/Jacquelyn Martin)

AP

President Barack Obama speaks in the South Court Auditorium on the White House complex, Monday, Sept. 16, 2013, in Washington. Before speaking about the economy Obama commented on the WashingtonNavy Yard shooting. (AP Photo/Carolyn Kaster)

AP

U.S. Capitol Police personnel keep watch on the East front of the Capitol as the investigation continues to the shooting at the nearby Washington Navy Yard Monday, Sept. 16, 2013, in Washington. At least one gunman opened fire inside a building at the Washington Navy Yard on Monday morning. (AP Photo/J. Scott Applewhite)